Variable nebulae report, 2020–2023

2024 December 9

Grant Privett & Richard Sargent

Due to their unpredictability, variable nebulae have, in recent years, become popular observing targets among some members of the BAA Deep Sky Section. By examining images obtained by members and stored in the online BAA Gallery, as well as examples shared between active observers, we discuss the changes – or otherwise – observed in nine variable nebulae during the 2020–2023 period. This is the first of a chronological series of such reports.

Introduction

Variable nebulae are clouds of gas and dust associated with young stars or protostellar objects. They are generally small in angular size, typically being around 0.5–2 arcminutes across, and have been observed to change in appearance over human timescales of years, months or days. Only a small number are known, but it is highly likely others exist and would be observable in instruments belonging to today’s amateur. It is always worth checking your images of nebulosity – especially near molecular clouds – for unexpected changes.

As most are too faint for easy detection visually (Hubble’s Nebula is an exception), they are, primarily, CCD/CMOS objects. So, it is no surprise that they have grown in popularity as observational targets since the appearance of vaguely affordable CCD cameras in the ’90s, and their wider uptake in the mid-2000s.

Those discussed herein are the variable nebulae currently being reported/shared as observed by members of the BAA Deep Sky Section. Their observational history is described here in brief; in subsequent reports this will not be included.

There are seven core contributors who monitor the variable nebulae frequently, with a similar number contributing occasionally. Others wishing to contribute images – if only occasionally – would be very welcome. By imaging on multiple nights, quite soon you have a very deep image of the field – and these objects often lie on the edges of attractive faint nebulae.

The positions of the variable nebulae discussed in this report can be found in Table 1.

Observers

The following observers submitted digital images to the Section or shared them via the BAA Gallery during this reporting period:¹ Stephen Avery, David Boyd, Simon Dawes, Tim Haymes, Mike Harlow, Nick Hewitt, Nick James, Martin Mobberley, Callum Potter, Mike Paling, Grant Privett, Richard Sargent, David Strange, Bob Trevan, Ivan Walton, and Mazin Younis. The Gallery can be found on the BAA website and contains observations and images made and posted by members. Members can post any images relevant to astronomy and can establish their own ‘album’ of images. The Gallery can be searched for images of a particular object, or for images posted by a particular member.

The nebulae

Gyulbudaghian’s Nebula

The variability of this nebula was noted by two groups of observers,² the year after its discovery.³ It is associated with the young variable star PV Cephei and undergoes dramatic, unpredictable changes, which make it a great target for amateur imagers. When discovered, it showed as a thin, curved arc to the north-east, which later fanned out and brightened, forming a triangle to the north of the star, only to fade and brighten erratically over the years.

It has been quite active during this reporting period. Meanwhile, PV Cephei hovered between 16.5–17.5 mag, with the only major brightness excursions occurring between 2020 Jul and 2021 May.

The period started with only the curved arc faintly visible on the north-eastern edge of the nebula; this then faded by 2020 Oct (see Figure 1a, where PV Cephei is arrowed). As Nick James said at the time, ‘the nebula seems to have gone altogether now’. The part of the arc nearest PV Cephei then gradually became more visible and slightly more evident as 2021 started, remaining faint but growing in length by 2022 Jan. It then vanished entirely before the summer of 2022, with only hints of its presence until into 2023. May of that year saw the north-eastern arc again appear, plus a small stubby extension running north from PV Cephei. The northern extension became more evident / brighter and contained intriguing detail, while the arc to the north-east remained strong (Figure 1b). By October, the thin, faint arc from the star PV Cep sweeping north-east up toward the Herbig–Haro object had brightened, as had the odd, mottled patch of light appearing just above the star itself, with a possible extension to the west. The appearance of the nebula remained steady until the end of 2023.

On deep images, a patch south of PV Cephei remained visible but very faint throughout the period. This patch is believed to be caused by the other polar flow from PV Cephei.

New observers of variable nebulae may wonder how they can be confident that they are imaging deep enough to spot Gyulbudaghian’s Nebula. A simple rule of thumb is that, if you can clearly see the Herbig–Haro object – HH 415 – approximately 4 arcminutes to the north-north-east of PV Cephei, then you should detect Gyulbudaghian’s Nebula, if it is present. For many observers, this will require more than 45 minutes of total integration time, with over an hour necessary for some features.

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